Field of Invention
The present invention relates to a communication system, and more particularly to a communication system with a train bus architecture.
Description of Prior Art
Conventionally, due to the increased demand for product manufacturing process, an automation technology is widely used in a production process and the automation technology usually employs a plurality of serially connected input/output (I/O) modules to transmit a packet serial having data packets wherein a master/slave structure is used to transmit and process the packet serial with the data packets, which are forwarded to the I/O modules, by a serial bus interface protocol. In U.S. Pat. No. 8,531,942, entitled “COMMUNICATION SYSTEM HAVING A MASTER/SLAVE STRUCTURE”, which is filed on May 20, 2009, FIGS. 1A and 1B are schematic views of a communication system comprising a master-slave structure. Similarly, FIG. 1 is a schematic block diagram of conventional communication system with a master-slave structure. The transmitter unit TX of the control unit 13 in the primary unit 1 sequentially transmits the data packets to the first slave unit 3 (1) like an I/O module. The receiving unit RX1 of each slave unit 3 sequentially receives all the packets from the previous slave unit 3 wherein a processing unit 35 of a current slave unit 3 processes the packets, which belongs to the current slave unit 13, and the rest of data packets, which do not belong to the current slave unit 13, are forwarded to the next slave unit 3 by the transmitter unit TX1 of the current slave unit 13. After the last slave unit 3(N), i.e. stage “N”, transmits the rest of data packets to the receiving unit RX1 (not shown) of the central unit 20, the transmitter unit TX2 (not shown) of the central unit 20 transmits the rest of data packets back to the receiving unit RX2 of the last slave unit 3. Afterwards, the last slave unit 3(N), i.e. stage “N”, transmits the rest of data packets back to the previous slave unit 3, i.e. stage “N−1” (not shown), using the transmitter unit TX2, and the last slave unit 3, i.e. stage “N”, replaces a portion of the rest of data packets, which belongs to the slave unit 3, with the processed packet in the last slave unit 3 in a return path from the central unit 20 to the primary unit 1. Similarly, the transmitter unit TX2 of the slave unit 3, i.e. stage “N−1”, then transmits the collected packets to the previous slave unit 3, i.e. stage “N−2” (not shown), until the data packets in the return path are sent to the first slave unit 3. Finally, the primary unit 1 receives the processed packets of each slave unit 3.
However, the above-mentioned system requires two sets of transmitter units, i.e. TX1 and TX2 and two sets of receiving units, i.e. RX1 and RX2, to be installed in each slave unit 3 therein, thereby resulting in higher manufacturing cost of the system. Particularly, when the amount of the I/O modules is increased for the purpose of more and more manufacture processing nodes or stations, the quantity of the transmitter units and the receiving units will be considerably raised to increase the production cost. Furthermore, the response packets are inserted to the packet serial during the backward process, i.e. a returned procedure, from the central unit 20 to the control unit 13 via last slave unit 3(N) to first slave unit 3(1) and thus the response packets are not inserted to the packet serial during a forward process from the control unit 13 to the central unit 20 via first slave unit 3(1) to last slave unit 3(N), which results in the decreased transmission efficiency of the data packets. Consequently, there is a need to develop a communication system to solve the aforementioned problems.